Method and system for proving differences of light



Dec. 18, 1934. H, E EN 1,985,085

METHOD AND SYSTEM FOR PROVING DIFFERENCES OF LIGHT Filed June 14, 1929 2 Sheets-Sheet 1 Z 0 o 0:09; o 25 1 A TTORNEYS.

Dec. 18, 1934. H. H. GEFFCKEN El AL 1,935,035

METHOD AND SYSTEM FOR PROVING DIFFERENCES OF LIGHT Filed June 14, 1929 2 Sheets-Sheet 2 It'ili'l..."

mvsrrrons BLA W HTTOIPNEK Patented Dec. 18, 1934 UNITED STATES METHOD AND SYSTEM FOR PROVING DIF- FERENOES OF LIGHT Heinrich ii. Geffcken Leipzig, Germany, assignors to Radio and Hans R. Richter,

Patents Corporation, New York, N. Y., a corporation of New York Application June 14, 1929, Serial No. 811,029

' Germany August 31, 1827 I 13 Claims.

This invention is concerned with a method and with apparatus, for objectively ascertaining and determining differences of objects which are characterized by difl'erences in their quality of light absorption andlight reflection.

In order to facilitate the understanding of the invention, the prior art will first be briefly stated and the relations existing between the known and the wanted, and the present case will then be explained.

The trend and desire of industrial engineering to substitute the objective work of the machine for the subjective observation and endeavors of the human being is appreciably handicapped in all procedures-which require the assistance of the eye. It is, in principle, possible to carry out a great many observations and measurements, e. g., various technical controls; checking of operations; testing and sorting of materials, automatically, by the employment of light sensitive organs, such as selenium cells, photoelectric cells, thermocouples, etc., however, the existing solutions for these problems have seldom furnished satisfactory results, because of the weak currents furnished by the usual light sensitive organs, and on account of various sources of trouble connected with them.

The present invention proposes a safe and sure procedure serving to prove the existence of light differences, and it may, therefore, be utilized for indicating events and conditions which in some -manner or other are themselves based on light differences. a

The arrangements hitherto known, in which differences in light radiation are objectively de-- termined by the use of light sensitive electric organs, are limited to the observation, or, rather to say,qto the registration of differences in the current within the circuits of these organs. Change 'of current was, therefore, substituted for the diifernce of light, and the light comparison was accomplished by first determining the various light grades according to their absolute values, and then determining the light diflera ence by comparison of the various measured abs'oiute light .values. Such indirect procedures are always subject to error, and the errors multiply-with the number of steps in the process. A practical utilization of the mentioned methods is limited. This is also true in case *of improved arrangements in which the path of the light is directly switched from the object under observation to the object for comparison without complete shading to darkness, so that an inert mirror galvanometer connected in the indicator circuit retains its position in case of similarity oflight grades.

The grades of light for comparison are also brought to the indicator in temporal sequence, but the required change of the path of the beam directed upon the light sensitive organ takes place rapidly, so that the light differences which play upon the organ, cause current fluctuations in its electric circuit, which are so steep that they are separated from the simultaneously occuring direct currents, by means of transformers or condensers, etc. It' is negligible whether a condenser or 'atransformer is employed for accomplishing this separation of the alternating-current component which flows in the circuit of the light sensitive organ, and the direct current which occurs simultaneously. It is essential, however,

that secondary effects (energizaticn of relays or of signals) are only caused when an alternating current component occurs in the circuit of the light sensitive organ or, rather to say, when it disappears (zero method).

The switching of the light current to the light sensitive organ may be accomplished in various ways: by moving the light source or the light sensitive organ; or by moving the object under observation or one or more optical members which serve for directing the light, such as lenses mirrors, or shutters, etc.

The object of the present invention is to provide a light sensitive system for comparing light rays, which has. an increased sensitivity and dependability of operation.

A more specific object of theinvention is to provide a light sensitive system, in which an alternate and periodical cc'ntroloi' a photo-electric device is carried out by a light ray of standard intensity and a light ray whose intensity it is desired to determine, respectively, without the use of mechanically moving elements.

Another object of the invention is to provide a simple arrangement for comparing a plurality of objects, as to their optical properties, which is responsive to minute diflerences in optical properties, such as absorption, as compared to the arrangements-now being used in the art.

These and further objects of the invention will become more apparent by the detailed description which follows, taken with reference to the accompanying drawings, which, by way of example, illustrate, in a schematic manner, some forms in which the inventive idea may be embodied.

Figure 1 shows schematically an arrangement for comparing light intensities, in accordance with the invention.

Figure 2 illustrates an alternative system to be used in connection with Figure 1, by which the use of mechanically moving elements is avoided.

Figure 3 illustrates the application of the invention to a sorting or grading device.

Figures 4 and 5 show arrangements to be used in connection with the device according to Figure 3, using a glow discharge tube for indicating purposes.

Figures 6 and '7 represent schematically a complete sorting or grading system, comprising the arrangement according .to Figures 1, 3 and 4, and 1, 2, 3, and 4, respectively.

Similar reference numbers refer to similar parts throughout the different views of the drawings. g

The invention will now be explained with reference to the accompanying drawings, which show practical embodiments of light control systems using the new principles of the invention.

R ferring to Figure 1, we have shown two Nicol prisms 23 and 24 positioned perpendicularly to each other with reference to their polarization planes. Thecrosses indicate the light sources which are to be compared. The light rays emitted from them travel thru the Nicol prisms v23 and 24, respectively, and are then united in a known manner by means of the prism 25. They go then superimposed thru the rotating Nicol prism 28 and 25'. During the rotation of the analyzing Nicol prism 28, the light rays coming from the Nicol prisms 23 and 24 whose polarization planes are perpendicular to each other, will periodically pass and be extinguished with phase displacement. Since one light ray increases in intensity in the same relation as the other is diminished, this method affords a p.rfectly graded and quantitatively accurate exchange of two light paths. The alternating current component within the circuit of the light sensitive organ will disappear only when the two light intensities become equal.

An effect similar to, the one reached with the rotating Nicol prism 26 may be had without any moving parts, purely electrically, by using two Kerr cells known from the picture telegraphy art. In this case, the two Nicol prisms 23 and 24 are put in one plane and the analyzer 26 is adjusted to darkness. The Kerr cells are arranged between the prism arrangement 25 and the Nicol prisms 23 and 24, respectively, and are symmetrically energized under phase displacement. This is preferably accomplished by means of the pendulum circuit shown in Fig. 7. The two oscnlatory circuits .29 are energized by the alternating current source 32. They operate the two Kerr cells 27 and 28 which are excited by the battery 30 bridged by the condensers 31.

The economic importance of the new method above all lies in its adaptation to simple and safe automatic sorting of various objects.

By using comparative bodies, the present invention permits also continual automatic observation of variable optical properties. Several such arrangements which have proved practical will now be explained with reference to Figs. 3 to 5, inclulive.

In Fig. 3, the rectangle 34 represents the object under observation. This may be a plate, an

' opaque glass plate,'a plate-like light source, or

some reflecting medium, whose optical alterations are to be observed. The circular disk 35, carrying comparative bodies 33 with graded different color or luminosity, respectively, moves past said arrive at the light sensitive organ object. The light beam arrives perpendicularly to the arrangement as shown on the drawings, that is to say, the light beam moves periodically between the points 36 and 37. If the disk 35 is slowly turned in the direction of the arrow, the several comparative fields will pass, the object 34, and the alternating current component in the circuit of the light sensitive electric organ will disappear in the moment when the section on the disk agrees with the object 34. The indication is accomplished by means of the follow-finger ar rangement shown at the right of Fig. 3. The lever arm 38 moves synchronously with the disk 35. When a point is reached on which the color of the comparative body on the disk 35 agrees with that of the body 34, at which the alternating current component disappears, the arm 38 is released and the finger 40 stops. The finger now indicates on the dial 41 the section whose optical properties agree with the properties of the object 34. The indicator may, of course, be located distantly from the rest of the arrangemer t. However, means must in such a case be provided for synchronizing the disk 35 and the lever arm 38. If the path of the light beam is switched sufllciently fast in the arrangement shown in Fig. 3, the disk 35 may, accordingly, be operated faster, and an indicator. may be employed as shown in Figs. 4 and 5. In place of the finger 40, a glowtube 42 is used which is arranged radially on a rotating disk. The alternating current component occurring within the circuit of the light sensitive electric organ is transferred amplified or unamplified to this glowtube so that the electrode 43 in accordance with the amplitude covers a va-- -riable space, resulting'flnally in the picture shown in Fig. 5. The light band will appear smallest where the amplitude is smallest, that is to say. when the agreement has been reached between the optical properties of the object 34 and the secshades is possible when the comparative scale is provided with only those colors which are of practical value, provided a corresponding amplification of the alternating current component is taken care of. Attention may again be directed to the fact that false indications or errors in sorting, which are possible in connection with known sorting apparatus thru fluctuations of the light or on account of changes in the sensitivity of the light sensitive organ, are principally excluded with the present invention.

A further field for applying the new method isgiven in a variety of scanning apparatus and arrangements. For example, if the periodically switched, as it were, vibrating light beam of an arrangement is successively moved over drawings or objects, respectively, or l! these are moved under the lightbeam, every change of color, every contrast (line or border) will: cause an alternating current of varying duration within the circuit of the light sensitive electric organ. The

position of indicator fingers or marks, etc., mov-.

ing over a dial or scale, may also be determined and a release maybe effected in the moment when sorting system has been shown. As in Figure 3,v the body 36 under test is compared in succession with a number of standard bodies arranged annularly .on a rotating support 35 and having a predetermined gradation, in the example shown, of their light absorptive qualities or colors. The support 35 may be rotated by any known means, not shown on the drawings, for the sake of simplicity. The standard body 37 and the body under test 36 are supposed to be illuminated equally, such as by means of a common light source, omitted in this figure for ease .of illustration. The

; rays of reflected light of both bodies are passed through'polarizing Nicol prisms 23 and 24, respectively, and combined by prism 25 to act on a photo-electric cell 25 in the same manner as described in connection with Figure 1. A mirror or V reflector 23' is provided to change the original parallel direction of the reflected rays into directions perpendicular to. each other, for the subsequent combination by the prism 25. The prisms 23 and 24 are arranged'with their planes of polarization perpendicular to each other and the ana lyzing Nicol prism 26 is rotated at a speed substantially higher than the speed of rotation of the support 35, in accordance with the spirit of the arrangements described in Figures 1 and 3. The

' alternating output currents of the photo-electric cell supplied by the photo-electric system, indic'ated schematically at 45, serve to supply a neon tube 42, rotating synchronously with the support and indicating on a scale the bpdy which has equal optical'property with the body under test, such as shown in Figure 5. For this purpose, the neon tube 42 is arranged on a disc rotating synchronously with the support 35, in a manner similar to that shown in Figure 3 by dotted lines. Slip rings are provided to supply the photo-electric output current to the/rotating tube 42 through leads 46 and 47. t

It is obvious th at the system, as just described and illustratedby Figure 6, may be used for sorting purposes, instead of for indicating or measuring, as described.

, Referring to Figure '7, this is similar to the arrangement according to Figure 6, with the only difference that no rotating parts are used in the optical system, by providing, as polarization analyzers, two Kerr cells 27 and 28 in each ofthe light paths, operated by electric alternating potentials, with a phase difference of 180 degrees. By arranging the polarizing Nicol prisms 23 and 24 with planes of polarization being parallel and the analyzing Nicol prism 26 in the path of the combined rays with a plane of polarization perpendicularly thereto, the effect is obtained of an alternate and periodical action of the light rays on the photo-electric cell. The remaining part of the system is identical to Figures 6 and 2, which latter shows the electric converting circuit for producing the operating potentials for the Kerr cells from a single phase input; As is well known,

- a Kerr cell device consists essentially of 9. container filled with a specific chemical substance, such as nitro-benzol and two electrodes opposite to each other, similar to two condenser plates, whereby, with the'application of an electric voltage to the electrodes, the plane of polarization of a light beam passing the liquid will be rotated more or less dependent on the operating voltage applied.

What is claimed is:

1. The method ofdetermining the-intensity of light'rays, which consists in photo-electrically and alternately comparing, at a given frequency, said rays with rays of standard intensity producing and ascertaining the alternate current photoelectric response in accordance with the differenceof intensity of the rays being tested and the rays of standard intensity, respectively, at said given frequency and changing said standard intensity in predetermined succession at'a frequency lower than said first frequency.

2. The method of determining the optical properties of a body, which consists in photo-electrically and alternately comparing, at a given frequency, the optical property of said body with one of a plurality of standard bodies of predetermined gradation with regard to the optical property which it is desired to determine, producing and ascertaining the alternating current photoelectric response in accordance with the difference of the optical property of said body under test at a frequency lower than said first frequency.

3. The method of determining the optical absorption' of a body, which consists in photo-elec-' trically and alternately comparing, at a given frequency, the amount of light reflected from said body with the light reflected from one of a plurality of standard bodies of predetermined gradation as to their absorptive qualities; producing and ascertaining the alternating current component of the photo-electric response inaccordance with the difference of the absorptive qualities of said body under test and said standard bodies at said given frequency and exchanging said standard bodies in succession, at a frequency lower than said first comparing frequency.

4. In a system for determining optical properties of an object, comprising in combination a plurality of standard objects, having a predetermined gradation as to the optical property,

which it is desired to determine, an electro-optical device, means to vary the intensity of a light beam, corresponding to the difference in the optical property of said object and one of said standard objects, said light beam controlling said electro-optical device, further means whereby said variations take place periodically at a given frequency and means for exchanging said standard objects in succession at a frequency lower than said first frequency.

5. In a system for determining the optical absorption of an object, comprising-in'combination a plurality of standard objects, having different absorptive qualities, in predetermined gradation, an electro-optical device,- means to produce beams of reflected light, corresponding to the absorpfrequency.

6. In a-system for determining the optical absorption-of an object, comprising in combination .a plurality of standard objects, having different 4 absorptive qualities, in predetermined gradation, an electro-optical device, means to produce beams of reflected light, corresponding to the absorption of said object and one of said standard objects and Nicol prisms for polarizing said beams of light, with planes of polarization being perpendicular to each other, means for combining said beams to control said electro-optical device, a further Nicol prism arranged in the path of the combined beam and rotated at a definite speed and means for exchanging said standard objects in succession, at a frequency lower than the frequency corresponding to the speed of rotation of said Nicol prism.

7. Means for comparing the intensity of beams of light, comprising in combination means for producing a plurality of beams of standard intensity, in a predetermined gradation, an electrooptical device, means for polarizing the beam to be compared and one of said standard beams, with planes of polarization being at 90 degrees to each other, mea to subsequently combine both of said beams to control said photo-electric device, an anlyzing device with means for continuously rotating its plane of polarization at a given frequency and further means for exchanging said beams of standard intensity at a frequency lower than said first frequency.

8. Means for comparing the intensity of beams of light, comprising means for producing a plurality of beams of light of standard intensity, and predetermined gradation, a photo-electric device, Nicol prisms arranged in the path of the r beam to be compared and in the path of one of said standard beams, with planes of polarization being disposed at 90 degrees to each other, means for combining both of said beams to control said photo-electric device, a rotating Nicol prism in the path of said combined beam and means for exchanging said standard beams in succession at a frequency lower than the frequency corresponding to the rotation of said last Nicol prism.

9. Means for comparing the intensity of beams of light, comprising in combination means for producing a plurality of beams of different intensity gradation, a photo-electric device, means for polarizing the beam to be compared and one of said standard beams,.with planes of polarization being parallel to each other, Kerr cell analyzing devicesin the path of both of said beams, said Kerr cells being operated by analyzing electric potentials having 180 degree phase difference with respect to each other, means for subsequently combining both of said beams of light to control said photo-electric device, further polarizing means of said combined beam with its plane of polarization being perpendicular to 'the planes of polarization of the original component beams and means for exchanging said standard beams at a frequency lower than the frequency of said alternating potential supplied to said Kerr cell devices.

10. The method of determining the intensity of light which consists in periodically increasing and decreasing the intensity of a beam to be compared between maximum and zero at a definite frequency, periodically increasing and decreasing the intensity of astandard beam between maximum and zero at a frequency equal to said first frequency and at 180 phase difference therebetween, photoelectrically translating said beams, varying the intensity of said standard beam at a rate substantially lower than said frequency and ascertaining the disappearance of the combined alternating current photoelectric response of said beam corresponding to a definite intensity of said standard beam.

- 11. A system for determining the intensity of light comprising means for periodically decreasing and increasing at a definite frequency the intensity of a beam to be compared, means for periodically increasing and decreasing the intensity of a standard beam at a frequency equal to said first frequency and at a 180 phase difference therebetween, further means for varying the intensity of said standard beam according to a predetermined schedule and at a rate lower than said first frequency, means for photoelectrically translating said beams, and further means for ascertaining the disappearance of the combined'photoelectric response of said beams corresponding to a predetermined value of the intensity of said standard beam.

12. A system for determining the intensity of light, means for producing alight beam of standard intensity, a pair of polarizing Nicol prisms with their planes of polarization at a definite angle relative to each other, means for passing said standard beam through one of said prisms, further means for passing the beam to-be conipared through the other of said prisms, means for combining the polarized beams and an analyzing Nicol prism for the combined beam being rotated at a definite speed, and a photoelectric device controlled by the combined analyzed beam. 13. A system for determining the intensity of light comprising means for. producing a light beam of standard intensity, a pair of polarizing Nicol prisms arranged with their'planes of polarization at right angle to each other, means for passing said standard beam through one of said prisms, further means for passing a beam to be compared through said other prisms, means for combining the polarized beams, and an analyzing Nicol prism for the combined beam being rotated at a definite speed and a photoelectric device controlled by the combined analyzed beam. 

